In the data transmission industry the 100Base-T standard is an Ethernet wiring standard for Local Area Networks (LANs). The 100Base-T standard supports data transfer rates up to one hundred megabits per second (100 Mbps) over unshielded twisted pair copper wire cable or optical fiber cable. The 100Base-T standard is often referred to as “fast Ethernet.” The IEEE standard for the 100Base-T standard is IEEE 802.3u.
There are versions of the 100Base-T standard for three different cabling schemes. The first is 100Base-TX for two pairs of high quality twisted pair wires. The second is 100Base-T4 for four pairs of normal quality twisted pair wires. The third is 100Base-FX for multimode optical fiber cables. The 100Base-T standard is the most widely used Ethernet standard. The vast majority of implementations of the 100Base-T standard in use are 100Base-TX implementations. The 100Base-TX standard relies on one pair of wires for the transmit direction and relies on one pair of wires for the receive direction.
A line code is a signaling method that is used in a telecommunication system for transmitting information. One of the line codes that is used by the 100Base-TX standard is Multi-Level Threshold-3 (MLT-3) encoding. The MLT-3 encoding method uses three voltage levels. The voltage levels are designated “plus one” (+1) voltage and “zero” (0) voltage and “minus one” (−1) voltage. The MLT-3 encoding method will select one of the three voltage levels (or “states”) for the transmission of a data bit.
The MLT-3 encoding method will use either a “plus one” (+1) voltage level or a “minus one” (−1) voltage level to transmit a “one bit” (1). The MLT-3 encoding method will use a “zero” voltage level to transmit a “zero bit” (0). For example, assume that the current bit to be transmitted is a “one bit” (1). Then the MLT-3 voltage level will be a “plus one” (+1) voltage. If the next bit to be transmitted after that is a “zero bit” (0), then the next MLT-3 voltage level will be the “zero” (0) voltage level. If the next bit to be transmitted after that is a “one bit” (1), then the next MLT-3 voltage level will be the “minus one” (−1) voltage level.
To transmit a “zero bit” (0) the MLT-3 encoding method selects the “zero” (0) voltage level. To transmit a “one bit” (1) the MLT-3 encoding method will (A) select the “plus one” (+1) voltage level if the last “one bit” (1) was transmitted using the “minus one” (−1) voltage level, or (B) select the “minus one” (−1) voltage level if the last “one bit” (1) was transmitted using the “plus one” (+1) voltage level.
FIG. 1 illustrates the application of the MLT-3 encoding method to a sample binary bit sequence. FIG. 1(a) shows a clock signal 100. FIG. 1(b) shows a sample binary bit sequence 110. FIG. 1(c) shows a resulting encoded signal 120 that is obtained by applying the MLT-3 encoding method to the sample binary bit sequence 110.
There is a need in the art for a system and method that allows a user to send additional data over a 100Base-T Ethernet link while the 100Base-T Ethernet link is in operation. There is a need in the art for a system and method that allows a user to incorporate an additional low data rate data channel in a 100Base-T Ethernet link.